Detectability of Wandering Intermediate-Mass Black Holes in the Milky Way Galaxy from Radio to X-rays

Abstract

Intermediate-mass black holes (IMBHs, $10^{3-6}{\mathrm{M}}_{\odot }$), are typically found at the center of dwarf galaxies and might be wandering, thus far undetected, in the Milky Way (MW). We use model spectra for advection-dominated accretion flows to compute the typical fluxes, in a range of frequencies spanning from radio to X-rays, emitted by a putative population of $10^5{\mathrm{M}}_{\odot }$ IMBHs wandering in five realistic, volume-weighted, MW environments. We predict that $\sim 27\%$ of the wandering IMBHs can be detected in the X-ray with Chandra, $\sim 37\%$ in the near-infrared with the Roman Space Telescope, $\sim 49\%$ in the sub-mm with CMB-S4 and $\sim 57\%$ in the radio with ngVLA. We find that the brightest fluxes are emitted by IMBHs passing through molecular clouds or cold neutral medium, where they are always detectable. We propose criteria to facilitate the selection of candidates in multi-wavelength surveys. Specifically, we compute the X-ray to optical ratio (${\alpha }_{\mathrm{ox}}$) and the optical to sub-mm ratio, as a function of the accretion rate of the IMBH. We show that at low rates the sub-mm emission of IMBHs is significantly higher than the optical, UV and X-ray emission. Finally, we place upper limits on the number $N_{\bullet }$ of these objects in the MW: $N_{\bullet }<2000$ and $N_{\bullet }<100$, based on our detectability expectations and current lack of detections in molecular clouds and cold neutral medium, respectively. These predictions will guide future searches of IMBHs in the MW, which will be instrumental to understanding their demographics and evolution.

Accepted for publication in MNRAS. This is the final version of the manuscript. 11 pages, 7 figures. Includes predictions for Chandra, eROSITA, Planck, SCUBA, AXIS, Roman, CMB-S4, ngVLA

References in corpus (24)

• The James Webb Space Telescope
• The eROSITA X-ray telescope on SRG
• An ultra-luminous quasar with a twelve-billion-solar-mass black hole at redshift 6.30
• Advection-Dominated Accretion and the Black Hole Event Horizon
• Rapid growth of seed black holes in the early universe by supra-exponential accretion
• Slim disks around Kerr black holes revisited
• Compression and ablation of the photo-irradiated cloud the Orion Bar
• The Disc-Jet Symbiosis Emerges: Modeling the Emission of Sagittarius A* with Electron Thermodynamics
• The High Latitude Spectroscopic Survey on the Nancy Grace Roman Space Telescope
• Wandering Black Holes in Bright Disk Galaxy Halos
• Ab Initio Horizon-Scale Simulations of Magnetically Arrested Accretion in Sagittarius A* Fed by Stellar Winds
• X-rays across the galaxy population I: tracing the main sequence of star formation
• Intermediate-mass Black Holes from High Massive-star Binary Fractions in Young Star Clusters
• X-ray Detected AGN in SDSS Dwarf Galaxies
• Understanding star formation in molecular clouds II. Signatures of gravitational collapse of IRDCs
• Origins and Demographics of Wandering Black Holes
• The Radiative Efficiency and Spectra of Slowly Accreting Black Holes from Two-Temperature GRRMHD Simulations
• Toward determining the number of observable supermassive black hole shadows
• Unveiling the Population of Wandering Black Holes via Electromagnetic Signatures
• On the Formation of Molecular Clumps in QSO Outflows
• The Active Fraction of Massive Black Holes in Dwarf Galaxies
• Hunting for wandering massive black holes
• Dynamics of Intermediate-Mass Black Holes Wandering in the Milky Way Galaxy Using the Illustris TNG50 Simulation
• Accessing Intermediate-Mass Black Holes in 728 Globular Star Clusters in NGC\,4472

Cited by in corpus (10)

• The Lunar Gravitational-wave Antenna: Mission Studies and Science Case
• Dwarf AGNs from Variability for the Origins of Seeds (DAVOS): Intermediate-mass black hole demographics from optical synoptic surveys
• Orbital and Radiative Properties of Wandering Intermediate-Mass Black Holes in the ASTRID Simulation
• CLEAR: Spatially Resolved Emission Lines and Active Galactic Nuclei at $0.6<z<1.3$
• Observational Signatures of Massive Black Hole Progenitor Pathways: Could Leo I a Smoking Gun?
• Accretion from Winds of Red Giant Branch Stars May Reveal the Supermassive Black Hole in Leo I
• Discovery of a Dense Association of Stars in the Vicinity of the Supermassive Black Hole Sgr A*
• Compact stellar systems hosting an intermediate mass black hole: magnetohydrodynamic study of inflow-outflow dynamics
• Cosmic wallflowers: the circumgalactic origins of isolated ultra-compact star clusters at $z>7$
• Tracing black hole and galaxy growth across environments since cosmic noon